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2. Prefix-to-AS Mapping Database

2. Prefix-to-AS Mapping Database​

The BGP speaker loads validated objects from the cache into local storage. The objects loaded have the content (IP address, prefix length, maximum length, origin AS number). We refer to such a locally stored object as a "Validated ROA Payload" or "VRP".

We define several terms in addition to "VRP". Where these terms are used, they are capitalized:

  • Prefix: (IP address, prefix length), interpreted as is customary (see [RFC4632]).

  • Route: Data derived from a received BGP UPDATE, as defined in [RFC4271], Section 1.1. The Route includes one Prefix and an AS_PATH; it may include other attributes to characterize the prefix.

  • VRP Prefix: The Prefix from a VRP.

  • VRP ASN: The origin AS number from a VRP.

  • Route Prefix: The Prefix derived from a route.

  • Route Origin ASN: The origin AS number derived from a Route as follows:

    • the rightmost AS in the final segment of the AS_PATH attribute in the Route if that segment is of type AS_SEQUENCE, or

    • the BGP speaker's own AS number if that segment is of type AS_CONFED_SEQUENCE or AS_CONFED_SET or if the AS_PATH is empty, or

    • the distinguished value "NONE" if the final segment of the AS_PATH attribute is of any other type.

  • Covered: A Route Prefix is said to be Covered by a VRP when the VRP prefix length is less than or equal to the Route prefix length, and the VRP prefix address and the Route prefix address are identical for all bits specified by the VRP prefix length. (That is, the Route prefix is either identical to the VRP prefix or more specific than the VRP prefix.)

  • Matched: A Route Prefix is said to be Matched by a VRP when the Route Prefix is Covered by that VRP, the Route prefix length is less than or equal to the VRP maximum length, and the Route Origin ASN is equal to the VRP ASN.

Given these definitions, any given BGP Route will be found to have one of the following validation states:

  • NotFound: No VRP Covers the Route Prefix.

  • Valid: At least one VRP Matches the Route Prefix.

  • Invalid: At least one VRP Covers the Route Prefix, but no VRP Matches it.

We observe that no VRP can have the value "NONE" as its VRP ASN. Thus, a Route whose Origin ASN is "NONE" cannot be Matched by any VRP. Similarly, no valid Route can have an Origin ASN of zero [AS0]. Thus, no Route can be Matched by a VRP whose ASN is zero.

When a BGP speaker receives an UPDATE from a neighbor, it SHOULD perform a lookup as described above for each of the Routes in the UPDATE message. The lookup SHOULD also be applied to routes that are redistributed into BGP from another source, such as another protocol or a locally defined static route. An implementation MAY provide configuration options to control which routes the lookup is applied to. The validation state of the Route MUST be set to reflect the result of the lookup. The implementation should consider the validation state as described in the document as a local property or attribute of the Route. If validation is not performed on a Route, the implementation SHOULD initialize the validation state of such a route to "NotFound".

Use of the validation state is discussed in Sections 3 and 5. An implementation MUST NOT exclude a route from the Adj-RIB-In or from consideration in the decision process as a side effect of its validation state, unless explicitly configured to do so.

We observe that a Route can be Matched or Covered by more than one VRP. This procedure does not mandate an order in which VRPs must be visited; however, the validation state output is fully determined.

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